Automatic electronic telephone system



July 24, 1962 A. H. FAULKNER AUTOMATIC ELECTRONIC TELEPHONE SYSTEM 15 Sheets-Sheet 1 Original Filed Aug. 23, 1955 w SS 25% Si.

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July 24, 1962 A. H. FAULKNER AUTOMATIC ELECTRONIC TELEPHONE SYSTEM Original Filed Aug. 23, 1955 l5 Sheets-Sheet 6 Fig. 6

July 24, 1962 A. H. FAULKNER 3,046,350

AUTOMATIC ELECTRONIC TELEPHONE SYSTEM Original Filed Aug. 23, 1955 l5 Sheets-Sheet '7 H/A/G//VG CO/WHOL MATH/X 750 IN V EN TOR. ALFRED H. @UL/(NER July 24, 1962 A. H` FAULKNER AUTOMATIC ELECTRONIC TELEPHONE SYSTEM Original Filed Aug. 23, 1955 YFU-($08344 15 Sheets-Sheet 8 FHG p, 820-/ REG/STER @2 U t M237 8/0 al 0 8230 8/7'/ ,ur/3J I I I fr-0 37'0 @Pgs PP P5 PPPP g5 P50 36/ y I l l PF4 l 'Vl/L7.' T p orf/Ef? H56. WSE HWG/6 GENE/M701? GENE/P470 l l 6 2 W7 MEN@ N "P W50 "Poo INVENTOR. ALFRED H UL/(NER Fly-6 W@ @4%.

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July 24, 1962 A. H. FAULKNER 3,046,350

AUTOMATIC ELECTRONIC TELEPHONE SYSTEM Original Filed Aug. 23, 1955 l5 Sheets-Sheet 9 T0 OTHER REGISTER FROM OTHER LINK. CIRS.

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AUTOMATIC ELECTRONIC TELEPHONE SYSTEM .mY F a `Iuly 24, 1962 Original Filed Aug. 23, 1955 July 24, 1962 A. H. FAULKNER 3,046,350

AUTOMATIC ELECTRONIC TELEPHONE SYSTEM Original Filed Aug. 23, 1955 15 Sheets-Sheet 12 WNS IN VEN TOR.

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u AQ m N @E July 24, 1962 A. H. FAULKNER AUTOMATIC ELECTRONIC TELEPHONE SYSTEM original Filed Aug. 2s, 1955 15 Sheets-Sheet 15 Loma INVENTOR. ALFRED H. FAULKNER BY W ATTY.

ite States This invention relates to automatic electronic telephone systems and particularly to an electronic telephone systemutilizing semiconductor diodes and transistors.

A general object of the invention is to provide an improvedvautomlatic telephone system for selectively establishing a two-way communication path between any two telephone lines in the system.

Another object of the invention is to vprovide an improved automatic telephone system utilizing semiconductor diodes and transistors to perform routing and switchmg operations.

Another object of the invention is to provide in an automatic telephone system transistor circuits responsive to line identifying signals for selectively completing connections between subscriber lines. Y

A further object of the invention is to provide van improved automatic telephone system employing time multiplex means forA signal transmission. The aspect of the invention relating to the multiplex signal transimission proper has been claimed in my co-pending application Serial No. 530,085, filed August 23, 1955, now Patent No. 2,931,863, of which the present specification is a division.

A further object of the invention is to provide an automatic telephone system having an improved electronic switching matrix for selectively connecting any one of the subscriber lines to available switching circuits.

A more specific object of the inven-tion is to provide an electronic telephone system having an improved switching matrix for connecting any one of the subscriber lines to available switching circuits on a pulse multiplex basis.

An additional object of the invention is to provide an improved ringing control circuit.

A more specific object of the invention is to provide an improved ringing control circuit particularly adapted to operatein a substantial-1y electronic telephone system.

A more specific object of the invention is to provide an electronic ringing control circuit substantially in the form of a matrix adapted to test any subscriber line in response to the application thereto of a corresponding timed identity pulse.

Another object ofthe invention is to provide improvedV operate in an electronic telephone system employing pulsemultiplex transmission means.

Further objects and features of the invention will be Y understood from the followingdescription `and drawings, forming a part thereof, wherein:

FIGS. l and 2 show in block schematic for-rn `an automatic telephone system inaccordance with the invention; FIGS. 3 through l0 comprise a detailed circuit diagram of-the telephone system illustrated-inFIGS. 1 and 2;

ice

FIGS. l2 and.l3 display a schedule ofthe voltage and V current transformations that takeplace in the telephone system responsive tothe initiation `of-a cell therein; and,

FIGS. 14 and 15 are schematic diagrams of alternativel circuits for use inthe telephone system of FIGS. 3 through l FIG. 16 is a schematic diagram of the two-way transmissionsystem according to the invention.

Section 1.--The General Arrangement of the Telephone System Referring more particularly to FIGS. land 2 whicharev joined'in end-'to-endrelationship for viewing purposes, there is shown therein in block schematic form, a telephone system operated on a step-by-step basis to establish selectively a two-waycomrnunication path between` any two `subscriber lines, for example, subscriber lines 301. and subscriber line 711, in a groupA of subscriber linesand to maintain a plurality of such communication paths at a time. The system includes' an in-switching matrix 450 which has access via the linecircuits, for example,

' the line circuits 320 and 720, to all of the subscriber linesf in the group including the subscriber lines 301 and 711 for connecting the calling Iones to .the common conductor.

the pairs calling tens and units registers of which only two pairs 810 and 830, and 810A land 830A are illustrated.

A register distributor. 910 continuously assigns an idle; :one of the pairsof registers tothe marking circuits'.

The individual pairs of registers operate to effect connection of the corresponding subscriber lines to the common conductor SM460 during selected periods .offral timed cycle'y which selected periods are reserved to the exclusive use oi' the register pair by the pulse generator 850.r

A number of link circuits 500, etc., which' are individually assigned to the pairs of registers and operated in synchronismtherewith by "the pulse generator 850,'eaoh recover the signa-ls of'one of the calling subscriber lines from the conductor SM460, identify the called subscriber line and transfer the connectionto the common conductor SM620. A ringing control matrix distributor 950-as` signs the identify of` a called line tothe ringing control matrix 750 on a one-at-a-time basis whereby theA calling subscriber line is tested for busy'or idle condition.

An out-switching matrixv 600 has access.l to all of the 1 subscriber lines in the group `and also to the conductor Sli/i620 for completing the connection between calling subscriber lines and called subscriber llines during the selected periods of each timedcycle.

A ringing machine 860U provides means for ringing! `any idle subscriber liueres-ponsive to the test thereoflL by the ringingcontrol matrix750.

Section 2.--The Apparatus Incorporatedv in 'the Telephone System The several subscriber lines 30.1, 711,etc., are provided with conventional station apparatus 300, 710', etcl.,.includ ing ringing tand speech equipment and 'line 'circuits 320',l

720,y etc. Assuming that the system, yas described hereinf after in detail, is'adapted-to; serve one hundred lines,

the subscriben lines thereof are identified by two digit directory numbers of which the drectorynumber for trarily; chosen-to be l1. The line circuits operate to Patented July 24, 1962 v complete a connection between the subscriber line and the iii-switching apparatus including the tens marking circuit 340 and the units marking circuit 360 and the irl-switching matrix 456 when the line is calling and to complete a connection between the out-switching apparatus including the ringing control matrix 750 and the out-switching matrix 660 and `the subscriber line when the line is called.

The tens marking circuit 340 and the units marking circuit 360 are common to all of the line circuits in the telephone system and each include ten intercon nected stages respectively numbered from l through which stages are operable one ata time over input conductors respectively corresponding to the stages. Thus, each of the stages in the ltens marking circuit 340 is connected via the corresponding input conductors LT-l, LT-Z, etc., to the groups of line circuits for which the tens digit of the directory number corresponds to the number of the stage. By way of example, the last or 0 stage in the tens marking circuit 34d is connected via tens conductor LT-0 in multiple to the line circuits (including the line circuit 320) of the subscriber lines for which the tens digit of the directory number is 0. Similarly, each of the stages in the units marking circuit 360 is connected via the input conductors LU-l, LU-Z, etc., to the groups of line circuits for which the units digit of the directory number of the subscriber lines corresponds to the number of stage. By way of example, the first or l stage of the units marking circuit 360 is connected via the units conductor LU-1 in multiple to the line circuits (including the line circuit 320) of the subscriber lines -for which the units digit of the directory number is 1.

In order to provide markings from the circuits, the tens marking circuit 340 includes the output conductors MT-l, MT-2, etc., respectively corresponding to the stages and which are connected to the corresponding groups of line circuits and to the multiple conductor trunk line MT extending to the calling tens registers 810, S-A, etc. Specifically, `the output conductor MT-O is connected to the trunk line MT and to the group of line circuits (including the line circuit 320) of the subscriber lines for which the tens digit of the directory number is 0. The latter connection activates the connected line circuits to permit the application of a calling line marking signal on the one of the calling line circuits to the corresponding one of the input conductors LU-l, LU-2, etc., extending to the units marking circuit 360.

In the units marking circuit, the output conductors MU-l, MU-Z, etc., are connected to the multiple conductor trunk line MU extending to the calling units registers 830, 830A, etc.

Thus, the initiation of a calll on subscriber line 301 causes `the tens conductor LT-O of the line circuit 320 to `be marked by a signalling voltage. The LT-U conductor extends to the 0 stage of a tens marking circuit 340 and when no other stage in the marking circuit is active, a signalling voltage is returned to the line circuit 320 via the tens marking conductor MT-0 to control the line circuit for applying a signalling voltage on the units conductor LU-l extending to the l stage of the units marking circuit 350. The 0 stage in the marking circuit 340 and the l stage in the marking circuit 360 are thereby -operated and responsive thereto to the conductors MT-O and MU-l extending to the calling tens and units registers via Ithe trunks MT and MU, respectively, are marked. In the calling registers, the identity of the one calling line is registered and the marking circuits are subsequently caused to be released from the line circuit of the one calling line in a manner to be described more fully hereinafter.

It is to be noted that the foregoing explanation of the marking of the identity of a calling line is predicated on but one subscriber line in the system initiating a call at any one time. The operation of the tens marking circuit 34@ and the units marking circuit 360 is the same even if more than one subscriber line should initiate a call at the saine instant except that the marking circuits 34h) and 36d provide :an order of preference, as explained more fully hereinafter, so that only one calling subscriber line can be identified therein at any one time.

The calling tens and units registers Si() and 839, etc., are arranged in pairs and in addition to registering the identity of a calling subscriber line, each pair selectivel;l operates the iii-switching matrix 450 to connect the corresponding calling subscriber line to the single conductor output lead SM460. In the exemplary telephone system there are ten pairs of individually numbered tens registers and units registers which are represened in FIG, l by the No. l calling tens register 810 and No. l calling units register 83%, and the No. l0 calling tens register MGA and the No. l0 calling units register 330A. Idle pairs of the registers are assigned to the marking circuits 349 and 366 on a one-at-a-time basis by a register distributor 9l0. The presence of ten pairs of registers permits the telephone system to handle ten calling lines at a time. The pairs of registers are sequentially activated in timed cycles by pulses applied thereto from the pulse generator S50 whereby the calling subscriber lines identiiied in any one of the pairs of registers are connected through the register controlled in-switching matrix 456 during the activation periods corresponding to the one calling register pair to the output lead SM460 on a time sharing, or time multiplex basis.

The in-switching matrix comprises a plurality of selectively operative crosspoints respectively corresponding to the subscriber lines in the system for interconnecting individual ones of the subscriber lines to the in-switching matrix output lead SM460. All of the pairs of calling registers having access to all of the cross points and each busied pair of calling registers operates, during its activation periods, the one crosspoint corresponding to the calling subscriber line identied in the pair of calling registers thereby connecting via the corresponding line circuit the calling subscriber line to the output conductor SM/itl. Immediately after the connection between the calling line and the lead 53h/i460 is completed, the line circuit is operated to remove the marking voltages from the marking circuits 340 and 360 whereby the marking circuits are released therefrom and prepared to identify another calling line.

By way of an example, assume that the calling subscriber line 301 is identiiied in the marking circuit 340 and 360 and that the corresponding directory number "01 is registered in the idle No. l calling registers 8l() and 836 arbitrarily assigned thereto by the register distributor 910. Responsive to the registration of the directory number 01 therein the No. l calling registers S10 and 830, which are activated in this time multiplex system for one fixed period out of every ten periods, for example, the first iive microseconds of a fifty microsecond period, operates during the ve microsecond activation periods, the crosspoint in the in-switchiug matrix 450 corresponding to the calling line identified by the "01 directory number. The operated crosspoint interconnects the matrix output lead SM450 with the calling subscriber line 301 via conductor 1.401 and the line circuit 320. As soon as the calling subscriber line is connected through to the matrix output conductor SM460, the marking voltage in the line circuit 329 is removed from the LT-tl conductor thereby releasing the marking circuits 34() and 360 and rendering the marking circuits available to identify other calling lines.

The conductor SMM@ has access to a plurality of link circuits 596, 569A, etc., respectively corresponding to the pairs of calling registers which link circuits are correspondingly numbered and cyclically activated in synchronism with the corresponding pairs of calling registers. Thus, for example, the No. 1 link circuit 500 is associated with the conductor SM460 during the same live microsecond intervals that the corresponding No. l calling registers 8,10 and 83s?? connect the subscriber line 301 to the conductor SM466.

Each of the link circuits has a plurality of individual circuits corresponding to those shown in detail inthe No. 1 link circuit 500 of FIGS. 5, 6 andk l0 including an input control circuit513, a holding circuit 514, sequence switch 540, tens counting chain units counting chain 1G50 and a switch-through circuit 650. Common to all of the link vcircuits are the ringing control matrix distributor 950 and a ringing control matrix 750.

In each of the link circuits, the directory number dialled at the corresponding calling subscriber station is recovered and registered. For example, assuming that the subscriber line 30.1 initiates a call to the subscriber line 7M identiiied by the directory number 11, the INo. l link circuit 500 recovers and registers the directory number ll transmitted to it via the in-switching matrix 450 and the conductor SM460. Responsive to registration of the dialled directory number in the link circuit 5%, the called subscriber line 71, identified by the dialled directory num ber, is tested to determine whether the line is busy or idle. This testing is -accomplished through .a ring control matrix 75!) which is connected directly to the line circuit 720 of the subscriber line 71.1 via the conductor RC-11 in `the multiple conductor trunk line RC. The link circuits identifying the called subscriber lines are assigned to the ringing control matrix 750 on a one-ata-time basis by the ringing control matrix distributor 950.

If the called line 711 identified in link circuit 580 is found to be idle by the ringing 'control matrix 750, the ringing machine 861) is connected to the line circuit 72@ thereof via the ringing generator leads RG-ll and RG-Z. Further, in response tothe answering of the call at the called line, the crosspoint in the outswitching matrix out) corresponding to the called subscriber line '7M is operated in synchronisrn with the activation of link circuit 500 so that the conductor SM464] is connected via the link circuit 500, conductor SM620, the out-switching matrix 600, the conductor Ltll and the line circuit 720 to the subscriber lline 711 during the five microsecond intervals that the calling subscriber line 3M is connected to the 'conductor SM460. In `this manner a connection is completed from the calling subscriber line 301 to the called subscriber line 711.

Should the called line 711 be busy, the link circuit 599 is caused by the ringing control matrix 750 to return a busy signal to the calling line 250i over the line SM466, whereupon, the party at subscriber line 301 may release the connection.

To better understand the rhode of operation of the. individual circuits in the system, reference will now be made to the FIGS. 3 through 10 arranged as shown in FIG. 11. By Way of introduction to the FIGS. l3vthrough 10, it will be noted that the telephone system is essentially electronic and includes diodes and transistors. The transistors and diodes used in the circuits are preferably of a crystalline type of a semi-conductor material, such as, for example, germanium. The diodes are identified in the drawings by the conventional symbol wherein the electric current flow (as distinguished from electron cur rent iiow) is from the anode electrode thereof in the direction of the arrow to the cathode electrode. The transistors used in the circuits are preferably `of .the junction type and as may be noted from the conventional symbols employed `are of n-p-n semiconductor construction (the arrow on the emitter electrode is pointed away from the base) and of p-n-p semi-conductor construction (the arrow on the emitter electrode is pointed towards the base). The direction of the arrow defines the direction of electric'current flow through the emitter.

The features of the telephone system in accordance with the invention will be understood from the following detailedI explanation ofthe operation ofthe system as shown in FIGS. 3 through l0 and by considering rst the initiation of a call at the. station 3th) on the subscriber line 3M'.

Section 3.-!niiation of a Call at the Station 300 As shown in FIG. 3, each or the subscriber lines 301, etc., comprises a pair of line conductors 301A and 301B, etc., having connected thereacross a calling station 300, etc. The apparatus in station 3M is conventional and includes the telephone instrument 312 and the d-ial mechanism 3&6 including the impulse springs 317 shunted by the resistor 318 and the dial off-normal springs 319. Ad- Y ditionally, the station `apparatus includes the switch hook 311.3, the switch hook springs H3A and 313B and the ringer 3?5 with its associated D.C. blocking capacitor,

Assuming that all of the subscriber `lines 35H, 711, etc., are idle, none of the circuits in the system'are operative other' than the register distributor 910 which as preselected and assigned, for example, the idle No. l calling registers Siti and 33t? to the marking circuit 349 and 36u, respectively. The current flow through the subscriber line 36d at this time to is interrupted, which current flow is illustrated by the curve 126i. in FIG. 12.

When at the time t1 the party at station 300 removes the telephone instrument 312 lfrom the switch hook 313 for the purpose of initiating a call, a circuit is completed -from -48 volts in the yline circuit 32u through the resister 332A, the upper primary winding of the transformer TR-1, the contacts 331A, conductor 301A, telephone instrument 312, switch hook contacts 3113A, conductor 3MB, contacts 331D, the lower primary winding of the transformer TR-l and the resistor 332B to ground potential. The values of resistors 332A and 332B are balanced with respect to the impedance of the subscriber line and the telephone instrument 312 so that when the circuit is completed, the current ow therethrough will establish at the junction between resistor 632B and the lower vn'nding of the transformer TR-l at -24 volts. inasmuch as DC. loop impedance of the subscriber line .Stil and the station 330 may vary, the junction between the resistor 332B and the lower primary Winding of the transformer 'FR-#1 is prohibited from going more negative than -24 volts by the 24 volt source connected thereto via the diode D327. Y This negative voltage on the one terminal of the resistor 332B is applied to the emitter of the transistor T329 thereby rendering this transistor conductive from ground potential via resistors 337A and 337B and through the base-emitter path thereof. The collector electrodeis thereupon clamped vat 24 volts ywhich voltage is extended to the junction between the resistors 323A and 328B and the diode D334. Responsive to the negative voltage at the junction, the cathode of diode D334 is biased conductive and the transistor T338 is biased at its conductive threshold. current 1iiow in the Iloop is DC. there is no current -flow induced in the primary winding of the transformer and the capacitor 336 connected from one terminal of the secondary winding to ground potential is not charged..-

As no current flow is provided through thesecondary winding or the `speech frequency shunting capacitor 335 connected between ground potential and the other terminal of the secondary winding to the base electrode of 301 as calling to the marking circuits 349 via the conducinasmuch as theannesso 7 tor LT-0 whereby the tens marking circuit 346 and the units marking circuit 35i? are operated.

Section 4,-Operrzlz'on of the Marking Circuits The tens marking circuit 340, and the units marking circuit 350 are identical and each include tcn stages operative one at a time of which only the first and last stages of each are illustrated in the circuit diagram of FIG. 3. As pointed out previously, each of the stages in the marking circuit is provided with a separate input and output A Conductor and is operated only over the inout conductor corresponding to the stage. Thus, in the teus marking circuit Siti?, tte first stage is connected in multiple via conductor LTEL to all line circuits for which tens digit of the directory number of the subscriber line associated therewith is l and the stage is therefore known as the l stage. Similarly, the input lead LT1@ to the last stage in the tens marking circuit 34h is contracted in multiple to the line circuits, including the line circuit 32%, for

which the tens digit of the directory number of the subscriber line associated therewith is O and the stage is therefore known as the 0 stage. The stages in each ot the marking circuits are so interconnected that only one stage in each marking circuit may be operative at any given time.

Referring specifically to the tens marking circuit 340, the transistors T3424 through T3424) and T3484 through Ta-tS-G in the stages thereof are normally conductive when no marking is applied to the input conductors thereof and the transistors TEM-l through TSM-0 are normally nonconductive whereby no marking is applied to the output conductors of the stages. Responsive to 'the above described marking on the diode D334 in the line circuit 320, current iiows in the conductor LT-t from the 0 stage thereby operating the 0" stage in a manner described hereinafter and indicating that one of the subscriber lines for which the tens digit of the directory number 0 is calling. The input lead LTA to the stage is connected to a junction between the resistors 341A0, 3413-0 and MTC-ti, which junction is normally maintained at the ground potential via the resistor 3MB-0. At the time t1, the 24 volts applied to the cathode of the diode D334, renders the diode conductive causing current to flow therethrough and establishing the junction between the resistors SMA-0, 34134) and SMC-ti at 24 volts. The potential at this junction biases the base of the transistor T347-t) conductive via the resistor SMA-0 and diode DSM-0. The collector and the emitter of transistor T347-0 are thereby clamped at substantially 48 volts causing the transistors TSM-0 and T3434? to b come nonconductive at the emitter electrodes thereof. Responsive to nonconduction in transistor T3424), ground potential is removed from the collector thereof thereby changing the path of the current iiow from the base of the transistor Trti'-n to the conductor LT-ti to that path through diode D349-0 and the resistor SLi-TCW. The collector electrode of the now nonconductivc transistor TSaeS-tlis maintained at substantially ground potential whereby the base of the transistor T352 is rendered conductive and the emitter electrode is established at substantially ground potential. The ground potential on the emitter electrode or" T352 is further eX- tended to all of the diodes D'S- through DS-i-oti, thereby providing a lower impedance current path to the conductors LT-l` through LT-9 than is available through the nonconductive transistors T3474L through TBM-9. Thus, at the time t1, the 0 stage of the tens marking circuit 340 is rendered conductive and all of the other stages of the marking circuit are temporarily rendered nonconductive and the output conductor MT-i from the 0 stage connected to the emitter electrode of transistor T3474? is at 48 volts potential as indicated by curve 1292 in FIG. i2.

The conductor MTL@ extends to the collector electrode mja Cil

similar transistors in all other line circuits for which the tens digit of the directory number is 0. Additionally, the conductor MT-t) extends to the assigned tens calling register 81% via trunk MT. It is assumed that the time t1, only the subscriber line 301 of all of the lines for which the tens digit is 0, is calling and therefore, only the transistor T338 in the line circuit 320 wiil be at conductive threshold. The 48 volts applied to the collector electrode of the transistor T333 by the conductor MT-t renders only that transistor conductive thereby clzrmping the emitter electrode thereof at 48 volts. As the units digit of the directory number of the calling line 36T is 1, the emitter of transistor T338 is connected via conductor LU-l to the first, or 1, stage, of the units marking circuit 360. In the "1 stage of the units marking circuit 360, the 4S volts applied to the lino LLLT renders the transistor T367-1 conductive and the transistors T 362-1 and T3634 nonconductive in the same manner as described above with reference to the "0 stage in the tens marking circuit 340. Additionally, therein, the coilector electrode of transistor T368-1 which is at this time nonconductive, is maintained at substantialiy ground potential through resistor 359A-1. This ground potential is applied to the collector electrodes of the succeeding transistors T3674 through T3674), thereby disabling those transistors and simultaneously biasing the emitter eiectrodes of the transistors T368-2 through Tli-Q nonconductive. Nonconduction in transistor renders the transistor T 372 conductive and establishes the emitter electrode thereof at ground potential, thereby disabling via the diodes D36S-2 through E365-ti, all of the stages 2 through 0. The 48 voits at the emitter electrode at the transistor T367-1 is applied to the output terminal MU-l which is extended to the units `calling register S30 via the trunk MU as shown on curve i253 in FIG. 12.

Should it happen that more than one of the subscriber lines, including subscriber line 381, for which the tens digit of the directory number is "0 be initiating a call at this time, the transistor T338 in the line circuit 32 and the correspondingly biased transistors in the other of the cailing line circuits will be rendered conductive by the 48 volts applied thereto over conductor MT-i. As a result, the conductor LU-l and the correspending conductors connected to the units marking circuit 360 will be marked by a 48 voltage. However, in this instance only the l stage in the marking circuit 3-56- wiii be operated because the stages therein operate one at a time as explained and the circuit establishes an order of preference proceeding from the "1 stage through the O stage. The other calling subscriber lines are delayed and identified according to the order of preference as the marking circuits 34) and 360 are released by the line circuits.

Thus at the time t1, the tens marking circuit 340 has identified by a marking on the MT-G conductor that a subscriber line for which the tens digit of the directory number is 0 is calling and the units marking circuit hasvsimultaneously identied by a marking on the MU-I conductor that a subscriber line for which the units digit of the directory number of 1 is calling. These markings on the MT-t) and MU-l conductors are extended to the assigned tens register 810 and units register 83%, respectively.

Section 5.--Operatiorz of the No. 1 Calling Registers As mentioned previously, it has been assumed that the registers Slt? and 2330 forming the No. l calling register pair were preassigned to the tens and units marking circuits S'vt and 366, respectively, by the register distributor 916. The method of assignment will be explained in detail iater. Each of the register circuits are made up of ten stages respectively corresponding to an output condoctor trema marking circuit. Thus, the calling tens regisrert has ten stages respectively connected to the MT-O, and the units register 830 has ten stagesrrespec- V tively connected to the units marking conductors MU-l through MU-0. In the circuit illustration of FIG. 8, only two stages of each' register are illustrated. Additionally, each of the stages in both ythe tens register 810 and the units register 830 are connected to the register distributor 910 by the conductor'RD-l. Responsive to the preselection by the register distributor 910 of the No.l l calling rregisters 810 and 830 for operation with the marking circuits 340 and 360 at the time t1, 48 volts is 'applied to the conductor RD-l by the register distributor 910. This voltage is connected to all of the stages inthe tens register 810 Via the resistors S17-1 through 817- and to all of the stages in the units register 830 via the resistors 843-1 through 843-0.

In the tens register 810, the conductors MT-l through MT-t)` apply groundrpotential to the corresponding stages via resistors 816-1 through 816-0, respectively, and the marked conductor MT-0applies -48 volts to the "0 stage via the resistor 816-0. Similarly in theunits register 8.30, the marked conductor MU-l applies -48 volts to the l stage thereof via resistor 838-1 and the otherconductors MU-Zthrough MU-0 apply ground potential4 to the corresponding stages via the resistors 838-2 through 838-0, respectively.V Thus, the voltage in the tens register 810 at the junction between resistor 816-0 and resistor 817-0 is -32 volts and the voltages at the corresponding junctions in the other stages of the tens register 810 is less than -24 volts. The sudden application of a potential greater than -24 volts (-32 volts) tov the capacitor S-0 causes a negative impulse to be applied to the base` of the transistor T 815-0 which momentarily renders that` transistor conductive. Responsive to the conduction, the emitter and collector electrodes are raised to ground'potential. At the same time, the negative pulse is applied to the collector of the transistor T813-0 via the resistor 814-0 and the base of the transistor T813-0 is raised to a potential intermediate `between ground potential and -48 volts by the collector of transistor T815-0 via the resistor 819-0 thereby rendering the transistor T813-0Aconductive and clamping the base and the collector of the transistor T815-0 at conduction v voltage. Thus, the transistor T813-0 locks the transistor T815-0 conductive when the latter has been triggered conductive by the applied negative pulse. The y-24 volts at the other stages in the tens register l810 is insuflicient to initiate conduction in the transistors associated therewith. With the transistor T815-0-conducting the anode of the diode D821-0 is held at-substantially ground potential via the resistor 823-0.` At the same timera positive pulse PPI of a'value in the order of l0 volts as shown in curve 21204y of FIG. l2, is applied from lthe pulse generator'850 to the anodes of diodes D821-1 through DS21-0 via the capacitors 818-1 through 818-0, respectively. Thus, at this time t1, the anodes of the diodes D821-1 through D821-9 -are at substantially -48 -volts and cyclically receive the FP1 pulsations which are not transmitted therethrough. At the same time the anode of diodeDSZ-Ois at substantially ground potential and cyclically receives the positive PF1 pulsations which are. transmitted therethrough to provide an output on .conducf tor RT-0 as shown in curve 1205 of FIG. 12.

Similar action takes place in the first, or "l stagek of thecalling units register 8301 whereby the transistors T837-1 and T836-1 are rendered conductive. The-48 volts onl the. collector electrode of '11836-1 isapplied to the cathode of diode D834-1 via the resistor 845-1. Additionally, the negative pulses NPl from the pulse generator 85.0and of a magnitudeintheorder of l0 volts and4 ofV simultaneous occurrence with, the pulses PPlas shown in diagram 1206l of FIG. 12, are applied to the cathodes pf` diodes D834-1 through 13834-0 viaV the capacitors 833-1 through 833-0, respectively. At this time t1, the cathode of the diode D834-'1 in the unitsV register 830is at substantially-48 volts andthe, applied negative pulsations NPl are.transmittedrheref. through to provide an output on conductor- RU-1 as shown in curve 1207 of FIG.` l2. At the Sametime',

the cathodes of the diodes D834-2 through yDSM-9` .are`

at .substantially ground potential.

The diodes D821-1 through DSM-0,015 thecallin I tens register,810 .-are rconnected at the cathodes thereof..i

RU-l through RU-0 act to operate corresponding crosspoints in the in-switching matrix 450.

Section 6.-Operati0n of the 11i-SwitchingA Matrix 450;

The in-switching matrix 450 comprises onerhundred crosspoints respectively corresponding to the subscriber lines in the telephone systemforcompleting a connectiont for any calling ones ofthe subscriber lines Vto. theswitch.-k ing matrix output lead SM460. Each of the crosspoints includes a pair of oppositely poled diodes such as,. for

example, 13404-1 and D40'5-1, a resistor such as 4636-1r connected from the junctionbetween the diodes to -48 volts and a transistor T4034 connected at its collector electrode to the junction between .the diodes and the resistor. The emitter electrode of the transistor is connected to the output terminal in the tens register 810V corresponding to the tens digit of Vthe directory number of the subscriber line to which the crosspoint. corre-V sponds. Thus, as the crosspoint referred to and `illustrated above corresponds to the subscriber line illfor,

which the tens digit of the directory number is Zero, the emitter electrode of the transistor 403-1vis connected to the output conductor of the 0 stage ofthe tens register, that is, the conductor RT-0via the resistor 407. As illustrated in FIG. 4, the emitter electrodes of the transistors .T403-1 through T403-0,l which are respectively associated with the crosspoints corresponding to the subscriber lines for which the tens digit of the direc tory number is zero, are all connected to the conductor.

RT-0 via a resistor 407; Similarly, the output conductor RT-0 from the` tensregister 810 is connected via, the resistor 497 to the emitter electrodes of the transistor y' T493-1 through `T49'3-,0 which are connected to the crosspoints corresponding to the subscriber linesV forY which the tens digit is nine. From these examples it .maybe seen that theA output conductors RT-Sdown through RT-l are respectively connected to the emitter electrodes ,of the .groups of transistorsto which the tens digits of the related subscriber lines correspond, Y

The base Velectrode of the transistor lT4034, like thev base electrodes of the` other transistors corresponding'. to the subscriber linesvforA whichsthe units digit of the..

directory number is one, is` connected to the output conductor RU-l of the .units register l830", which. conductor is connected to the l stage thereof. The output conductor RU-Z from the units register 830 is connected to the Y,base electrodes of the transistors T413-2 'through `T403-2 associated with, crosspoints for. which the corresponding subscriberlineshave a directory number for which the units digit is two. Similarly, the conductors RII-3 through RU-0 are connected to the base electrodes of the transistors `correspondingly associated, with the units digits of the directory number three through. zero. f Y

Responsive to, the. application ofv the potentials, onr the conductor RT-0 and on thevconductor*RU-1,- the,

transistor T403-1 is rendered conductive during the The selectively applied 

